Elastomeric films have for some time been used and discussed in the literature with regard to their applications in disposable products, such as baby diapers and adult incontinent devices. These elastomeric webs or films are used primarily in the body hugging portions of garments. In diapers, for example, elastomeric bands are typically used in the waistband portions such as discussed in U.S. Pat. No. 4,681,580, issued to Reising et al., and Lash, U.S. Pat. No. 4,710,189. Both of these patents describe the use of elastomeric materials which have a heat stable and a heat unstable form. The heat unstable form is created by stretching the material when heated around its crystalline or second phase transition temperature followed by a rapid quenching to freeze in the heat unstable extended form. The heat unstable elastomeric film can then be applied to the, e.g., diaper and then heated to its heat stable elastomeric form. This will then result in a desirable shirring or gathering of the waistband of the diaper. A problem with these materials, other than cost, is the fact that the temperature at which the material must be heated to release the heat unstable form is an inherent and essentially unalterable property of the material to be used. This extreme inflexibility can cause severe problems. First, it is more difficult to engineer the . other materials with which the waistband is associated so that they are compatible with the temperature to which the elastomeric member must be heated in order to release the heat unstable form. Frequently this temperature is rather high which can.potentially cause significant problems with the adhesive used to attach the elastomeric waistband, or, e.g., the protective back sheet or top sheet of the diaper. Further, once chosen the elastomer choice can constrain the manufacturing process rendering it inflexible to lot variations, market availability and costs of raw materials (particularly elastomer(s)), customer demands, etc.
Other materials and methods have been proposed. For example, Berger, U.S. Pat. No. 3,694,815, proposed a method for attaching a stretched relaxed elastic ribbon to a garment by stretching conventional elastic ribbons and immediately freezing the elastomeric material at relatively extreme low temperatures (e.g., well below ambient). This process would obviously severely constrain the processing conditions and materials which could be used when attaching the elastomeric strand to its backing. UK Pat. Application 2190406 A proposed maintaining a conventional elastomer in a stretched condition, while attaching it to the member to be shirred (e.g., a diaper), by a rigidifying member, which would then be removed or destroyed following the attachment procedure. As described, the elastomers are first stretched then applied to the rigidifying member in its stretched form. Finally, Matray et al., UK Pat. 2,160,473, proposes an elastomer which will shrink at an elevated temperature (e.g., at or above 175.degree. F. or 79.4.degree. C). The allegedly novel feature of this material, compared to the heat shrink materials discussed above, is that it does not require preheating during the stretching operation but rather could be stretched at ambient temperatures by a differential speed roll process or by "cold rolling". The polymer proposed was a copolymer having alternating segments of polyamidepolyether block polymers, commercially available under the trade name Pebax, particularly Pebax Extrusion grades 2533 and 3533. As an alternative, this patent application proposed placing a thin EVA(ethylene vinyl acetate) layer(s) over the elastomer by, e.g., coextrusion. The skin layer is chosen to prevent blocking or to be compatible with a later applied adhesive. It was noted that this layer can also produce a pleasing hand, but should not interfere with heat shrinkability.
Problems with these elastomeric films include the difficulties inherent in applying a stretched elastic member to a flexible substrate such as a disposable diaper. Although some of the elastomers proposed have the advantage that they can be applied at ambient conditions in a heat stretched unstable form, subsequent, often extreme, heating is required to release the heat unstable form to a contracted heat stable form. The temperature of this heat release is generally inflexible as it is determined at the molecular level of the elastomer. As such, the other materials applied to the elastomer, and the process conditions at which the elastomer is used, must be carefully selected to be compatible with this heating step.
Elastomers also exhibit relatively inflexible stress/strain characteristics which cannot be chosen independently of the activation temperature. Materials with a high modulus of elasticity are uncomfortable for the wearer. Problems with a relatively stiff or high modulus of elasticity material can be exaggerated by the coefficient of friction and necking of the elastomer which can cause the material to bite or grab the wearer.
In copending application Set. No. 07/438,593, filed Nov. 17, 1989, having a common assignee, there is disclosed an elastomeric laminate having at least one elastomeric layer and at least one skin layer which addresses the above problems in the art. In addition, the laminate has extremely useful and novel properties. When cast, or after formation, the elastomeric laminate is substantially inelastic. Elasticity can be imparted to the inelastic laminate by stretching the laminate, by at least a minimum activation stretch ratio, wherein an elastomeric material will form immediately, over time or upon the application of heat. The method by which the elastomeric material is formed can be controlled by a variety of means. After the laminate has been converted to an elastomer, there is formed a novel texture in the skin layer(s) that provides significant advantages to the elastomeric laminate.
Despite the numerous advantages in the materials of the copending application, there is room for improvement for some applications. In order to activate the nonelastomeric laminate into a state that will allow it to recover and become elastomeric, the laminate must be stretched a substantial amount for many materials contemplated as useful for the skin and core layers. This is problematic for some applications where low activation stretch ratios for the laminate would be desirable or where it is desired to obtain elasticity in specified areas.
The desirability of obtaining elasticity in specified areas of a ribbon or tape-like substrate is illustrated by U.S. Pat. Nos. 3,800,796, 4,834,820, 4,778,701 and 4,227,952, which disclose the use of composite materials designed to have specified areas of elasticity for use in diaper systems. However, these composites require complicated construction mechanisms to bring the diverse elements of the composite together and/or special procedures for their manufacture and use that limits their general applicability.